(1) Field of the Invention
The present invention relates to a solid-state imaging device and a manufacturing method of the same, and particularly to a technique for miniaturizing pixel cells that make up a solid-state imaging device.
(2) Description of the Related Art
In recent years, needs for high-pixelization of solid-state imaging devices have been increasing. To meet these needs for high-pixelization, a miniaturization of pixel cells that make up a solid-state imaging device has been advanced. As a result, it became difficult to separate pixel cells by local oxidation of silicon isolation (LOCOS) when considering processing accuracy (Refer to Unexamined Patent Publication No. 11-74499).
To solve the problem, as one example, a use of shallow trench isolation (STI) is proposed. The shallow trench isolation excels in microfabrications, and therefore, is expected to be suitable for separating miniaturized pixel cells.
However, the shallow trench isolation causes crystal defects due to process damages occurring in a manufacturing method and stresses of a silicon oxide film that is implanted in a trench. When electrons generated due to crystal defects enter into the photo diode, image defects such as dark currents and white scratches are generated.
To overcome this problem, a method of forming an impurity area of a reverse conductivity type to a photo diode (hereafter, simply referred to as the “impurity area”) has been created on one side of a photo diode that is connected to a trench. With this arrangement, it is possible to prevent unwanted electrons from entering into a photo diode.
However, forming an impurity area causes a diminishment of saturation characteristics and sensitivity characteristics. This problem is common in pixel cells whose size is 2.2 μm square or smaller. Therefore, solid-state imaging devices that comprise 2.2 μm square pixel cells have not been realized.